Floating bimetal thermostat



March 9, 1954 w A, RAY 2,671,837

FLOATING BIMETAL THERMOSTAT Filed June 29, 1950 2 Sheets-Sheei l wa/HM n. @m1,

JNVENTOR.

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March 9, 1954 w. A. RAY

FLOATING BIMETAL THERMOSTAT 2 Sheets-Sheet 2 Filed June 29 1950 INVENTOR.

Zw #Trae/Eff il? ll Patented Mar. 9, 1,954

FLOATING BIMETAL THERMOSTAT William A. Ray, North Hollywood, Calif., assignor to General Controls Co., a corporation of California Application June 29, 1950, Serial No. 171,070

4 Claims.

This invention relates to bimetal thermostats, and especially to thermostats adapted to control an electric circuit.

Such thermostats are in common use for controlling the operation of a heating system in response to temperature variations in a space. Thus, for heating a room, the thermostat may be adjusted to cause a gas burner to ignite when the temperature of the room drops appreciably below the temperature to which the thermostat is adjusted. Similarly, when the temperature appreciably exceeds the desired value, the flow of fuel to the gas burner is interrupted.

It is desirable that the making and breaking of the thermostat contacts be effected within a "ery narrow range. Accordingly, the contacts ure iioating; the position of the contact carried by the bimetal is gradually altered in accordance with the temperature of the bimetal. Accordingly, very slight variations in this temperature result in a change from closed to open position, and vice versa.

In such floating thermostats, foreign matter is aptto be deposited on the contacting surfaces. Now, under such conditions, it is necessary that the contacts be urged together by the bimetal with a stronger pressure before effective contact is obtained. Accordingly, a lower temperature than that desired is required to close the contacts, and the differential temperature between open and closed positions is increased to a disadvantageous extent. In addition, the floating contact very gradually increases its pressure on the stationary contact as the bimetal flexes; and this gradual pressure variation often sets up undesired microphonic eiects.

The introduction of a resistance due to the foreign matter on the contacts, as well as to the imperfect contact upon the relaxation of pressure between them, causes a slight heating eifect. This heating effect causes the thermostat to open the contacts sooner than they should, and recycling occurs too frequently.

It is one of the objects of this invention to overcome these ditliculties.

In order to accomplish this result, there is a provision immediately to increase the pressure on the contacts as soon as they touch. This increase in pressure effectively eliminates all microphonic effects.

YIt is another object of this invention to ensure that the contacting areas be maintained clean, and especially by a slight rubbing action as the contacts are urged together. Thus, accumulation of dirt or other foreign matter on the contactsis prevented.

The thermostat structure embodying the invention includes a small electromagnet that is connected preferably in series with the control circuit, and exciting a pressure on the contacts just as soon as these contacts engage.

Accordingly, it is still another object of this invention to provide an electromagnet that serves to supplement the pressure between the contacts whenever they close.

This invention possesses many other advantages, and has other objects which may be made more clearly apparent from a consideration of several embodiments of the invention. For this purpose there are shown a few forms in the drawings accompanying and forming part of the present specification. These forms will now be vdescribed in detail, illustrating the general principles of the invention; but it is to be understood that this detailed description is not to be taken in a limiting sense, since the scope of the invention is best defined by the appended claims.

Referring to the drawings:

Figure l is .a view, mainly in section, of one embodiment of the invention, the thermostat being in contact-closing position;

Fig. 2 is a View, similar to Fig. l, illustrating the contacts in open position; and

Figs. 3 and 4 are views, similar to Fig. 1, of modications of the invention.

The thermostat structure shown in Figs. 1 and 2 includes a supporting wall I which may be the Wall of a casing, or the like. Through an aperture in this wall extends a sleeve 2 having a shoulder 3 engaging the outer surface of the Wall I. This sleeve 2 is attached to the wall I by the aid of a bracket 5 having a threaded aperture engaging the threaded end 6 of the sleeve 2. Between the bracket 5 and the wall I are a washer 'I and the apertured end 8 of a bimetal member 9. In this manner, one end of the bimetal member 9 is anchored to a stationary part of the mechanism.

The bracket 5 carries a iiexible contact carrying arm IG. The lower end of the arm lil is attached irmly to the lower end of the bracket 5.

A contact member I I is carried by the free end of the flexible arm I G, and is insulated therefrom by aid of the insulation bushings i2. The contact area I3 is convex. The contact member II is fastened to the arm I5 by riveting the end I4 over a terminal member I5 which serves to provide a connection to the contact member II Adjustment of the position of contact member II is afforded by a screw I6 engaging internal threads at the right-hand end of the sleeve 2, and bearing against the riveted end I4 of contact II. Turning of the screw in either direction causes corresponding movement of the contact member I I. This screw is conveniently manipulated by a manual dial 4 in the usual manner, and which is rotatably mounted on the sleeve 2 and joined to the screw I6, as by the aid of a dished plate I'I. This dshed plate I'I is coupled to the screw I3v below the head I8, as by the aid of the serrations I9.

Manipulation of the manual dial 4 adjusts the temperature at which the thermostat contacts open and close.

'I'he bimetal member 9 has a bend 20,. and the free end 2| carries the movable contact member 22. This movable contact member 22 is provided with a head 23. The shank of the contact member may be riveted over to form the head 24. Insulation bushings 25 serve to insulate this movable contact member 22 from the bimetal member 9. A terminal member 25 is disposed below the head 23 to provide appropriate connections.

That portionof the bimetal member 9 which extends from' the anchored end 3 slopes downwardly toward the right, and the other leg 2T of the bimetal member 3 is correspondingly sloped to the free end 2|'.

Asfthe bimetal member 9 iiexes about the bent portion 20, the direction of movement of the contact member 22 is oblique to the contacting surfaces of the members II and 22. there is a very slight rubbing action which keeps the contact surfaces clean and free of foreign matter.

In floating thermostat contacts of this character, the movement between open and closed position ofv the bimetal member 5 is very slight, and. is of the order of a millionth of an inch, or from about one-half of a millionth of an inch to one millionth of an inch. The rubbing movement, being transverse to the engaging niovefr ment between the contacting surfaces, is extremely slight, but it is nevertheless sufficient to maintain the contacts in operating condition.

In order to urge the contacting surfaces firmly together, as soon as contact is established, use is made of an electromagnet structure which affects the free end 2| of the bimetal member 9. Thus, mounted upon the bracket 5, above the screwy IS, there is a magnetic core 23!v having a pole piece 29. This magnetic core 23 may be at- 5 tached to the bracket 5, as by the aid of the shank 30 which may be riveted over the bracket 5 at its free end. An electromagnet coil 3i is mountedk en the core 28. The free end 2I of member 3 approaches closely to the pole piece 29. The electromagnet is energized through the contact members IIA and 22, as by the aid of the connection 32 which extends from the terminal I5v to one end of the coil 3 I.

Accordingly, just as soon as 4a light contact is effected, the pole piece 2S exerts a magnetic force upon the free end 2I of the bimetalmember 9, pulling this free end inwardly to press the contacting surfaces together. In the attracted posi'- tion, the air gap between the bimetal end 2| and the pole piece 29 may be of the order of one onehundredth of an inch. By providing this air gap,` even a slight iiexure of the bimetal 9` outwardly is suilicient to deenerg'ize the coil 3'I.

The coil 3|' may be placed in parallel with the circuit controlled by the thermostat contacts, and it sso designed to utilize a few izilliwatts of electrical power.4

The insulation sleeves I2 and 25 are quite'thick.l s0 as vto retard the'transmissionof heat from the Accordingly,

contact members II and 22 to the bimetal member 9. Accordingly, there is no substantial anticipating action which may occur by heating the bimetal elements.

In the form shown in Fig. 3, the bracket 5 and the spring arm I0 are similarly arranged to the form of Figs.- l and 2 in relation to the manual adjusting knob 4'. The supporting elements of the structure are omitted, but they may include the members shown in Fig. l. In this instance, the bimetal member 33 is made straight, and has a1 bend 341 to provide a leg 35 parallel with the anchored portion ofthe bimetal member 33. The contact member 36 is similar to contact member II, except that its contacting point 31 is made tapered. lThis contacting point cooperates with the contacting head 38 of a movable contact member 39.y This movable contact member, in this instance, is mounted on an upset portion 40 of the leg 35, said upset end being at an angle with respect tothe axisof the contact 36.

As the bimetal member 33 Iiexes aboutV the bent portion 3d, the contacting surfaces" have an' 0b"- lique motion with respect to the contacting surfaces, This is dueto the angular 'position of the upset portonllt.

As before, the free end 4I of the bimetal member is affected by the electromagnet coilY 31' tol urge the contacts together just asY soon as' these' ccntacts engage.`

In the form shown in Fig. 4,. the bimetal mem'- ber il is arranged as in the form shown in Fig. l, and carries the movable contact 22 in the same manner. The oblique direction of movement of the contact' member 22 is eiiectedby the sloping` legs of the bimetal member' 9,. as described in connection with Fig. 1.

In this instance, the electrornagnet coil 42 is disposed in a magnetic shell 43` providing an annular pole face likt. The shell 43 has a re-entrant portion le forming a recess terminating in aI wall Il@ that is apertured to accommodate the contact member Il?. This contact member 41 yis insulated from the' shell 43 by the aid' of the insulation sleeves el?. In order to complete the shell? structure, a magnetic member' (il) is utilized whichV is attached to the wall (i6 bythe aid of the con-l tact member El, the shank'of which is riveted over the 'terminal I5.

In this instance, the contact 3T is supported by the aid of the re-entrant portion 45` on theV shell 3 on the adjusting screw This adjusting. screw extends into an insulation cup 5B whichisl telescoped within the re-entrant portion 45.

, Manipulation of the dial 4 thus causes a. corresponding adjustment of the contact 4T.. When the screw I5 is withdrawn, the bimetal member 9 and contact 22 serve to urge the shellr 43 andh the cup' 55 against the end of the adjusting screw le.

The free end ZI' of the bimetal member 9l is influenced by the polar area i3 and the shoulder `tI formed by the member 49'. Asbefore, the elec'` annular polar area, and a` coil in said shell; the` shell having atubular `'central recess around which the coil is disposed, and said recess opene uw '4444A ing on that side of the shell opposite the polar area; means insulatingly supporting the second contact on the end wall of the recess; said polar area being opposed to the free end of the bimetal member; an insulation cup within the recess; and an adjusting screw extending into the cup.

2. In a thermostat: a bimetal member anchored at one end; a rst contact carried near the free end of the member and having a contacting surface; and a second contact adapted to be engaged by the rst Contact; said bimetal member being bent about an axis transverse to the length of said bimetal member and adjacent said first contact for inclining said surface of said first contact With respect to the direction of movement of said first contact, to provide a component of rubbing movement between the contacts immediately upon engagement therebetween.

3. In a thermostat: a bimetal member anchored at one end; a iirst contact carried near the free end of the member; and a second contact adapted to be engaged by the first contact; said member being bent about an axis transverse to the length of said bimetal member and adjacent said iirst contact that causes movement of the free end to occur in a direction oblique to the contacting surfaces of the contacts immediately upon engagement between the contacts.

4. In a thermostat: a support; a flexible element secured at one end to the support; said exible element having a free end spaced from, and extending in superimposed relationship with respect to said support when said flexible element is unflexed; said flexible element being arcuately movable; a rst contact member carried at said free end of said iiexible element; a generally U- shaped bimetal member; a second contact member having a contacting surface and carried on one arm of said bimetal member at a place spaced from the end of said one arm; means securing the other 'arm of said bimetal member to said support to substantially align said contact members; said one arm of said bimetal member extending on that side of said flexible element remote from said support; an adjustable abutment mounted by the support and engageable with said flexible element, said abutment being movable in a direction to flex said exible element arcuately toward said one arm of said bimetal member; said bimetal member being bent about an axis transverse toy the length of said one arm at a place along said one arm on that side of said second contact member remote from the end of said one arm, said bent arm inclining said contacting surface with respect to the direction of movement of said second contact member to provide a component of rubbing movement between the contact members immediately upon engagement therebetween; said free end being bent in a direction away from said rst contact member; and an electromagnet carried by said support and having a polar area substantially aligned with the said end of said one arm.

WILLIAM A. RAY.

References Cited in the iile of this patent UNITED STATES PATENTS Number Name Date 1,804,748 Derrick May 12, 1931 1,832,761 Brady Nov. 17, 1931 1,833,594 Russell Nov. 24, 1931 1,938,929 Petersen Dec. 12, 1933 1,992,765 Petersen Feb. 26, 1935 2,321,338 Ulanet June 8, 1943 2,381,557 Ray Aug. 7, 1945 2,413,100 Crise Dec. 24, 1946 

